Skylon: Promising Tests of the SABRE Engine

by Paul Gilster on December 3, 2012

The news from Reaction Engines Ltd. about its air-breathing rocket engine SABRE is interesting not only for its implications in near-term space development, but also for its pedigree. Reaction Engines grew out of British work on a single-stage-to-orbit concept called HOTOL ((Horizontal Take-Off and Landing) that was being developed by Rolls Royce and British Aerospace in the 1980s. Initially backed by the British government, HOTOL lost its funding in 1988, prompting Alan Bond’s decision to form the new company, which would continue the work with private funds.

The name Alan Bond should ring many bells for Centauri Dreams readers. Bond was a key player in and leading author of the report on the British Interplanetary Society’s Project Daedalus, the ambitious 1970s attempt to design a starship based on fusion propulsion. One thing the extensive Daedalus effort made clear was that a future attempt to reach the stars could only take place within the context of a Solar System-wide infrastructure, one that would have the ability to mine the atmospheres of the outer planets for the needed helium-3 and other resources. It’s no surprise, then, that Bond’s attention should now be on that infrastructure and how to build it.

For one craft SABRE is intended to power is a reusable spaceplane called Skylon that would reach orbit in a single stage, lowering the cost per kilogram of payload substantially, perhaps to as little as $1000 or less. As presented by Reaction Engines, Skylon is anything but another Space Shuttle. It would take off from a conventional runway, accelerating to Mach 5.4 at 26 kilometers altitude before switching its engines over to internal liquid oxygen mode to take the craft to low-Earth orbit.

The project’s backers say they can carry up to 15 tonnes into orbit aboard the unpiloted craft, a payload that could also, using a habitation module, be comprised of up to 30 astronauts in a single launch vehicle. Upon delivery of its cargo or complement of astronauts, the vehicle would re-enter the Earth’s atmosphere and land back at the runway, undergoing inspection and any needed maintenance before, within two days, being returned to the flight line. If Skylon can live up to this ambitious scenario, then it will have given us what the Space Shuttle promised — reusability with quick turnaround — in a far more flexible and much less expensive design.

Much comes down, as you can imagine, to the SABRE engine. The acronym stands for Synergistic Air-Breathing Rocket Engine, a design that combines a turbo-compressor with an air pre-cooler that at high speeds can cool hot compressed air that will then be fed into the rocket combustion chamber, where liquid hydrogen will form the other part of the mixture to be ignited. The pre-cooler technology is the key. It allows the incoming airstream to be cooled from over 1000 degrees C to minus 150 C in less than 1/100th of a second without any frost blockage.

SABRE thus works initially in air-breathing mode, using the atmosphere as its source of oxygen for burning with the liquid hydrogen in the rocket combustion chamber. Once above the atmosphere, the craft makes the transition to conventional on-board liquid oxygen. The dual approach means that a vehicle like Sylon could save over 250 tons of on-board oxidant — no huge first stage that has to be jettisoned as soon as the oxidant is used up . The pre-cooler work is critical because in its air-breathing mode, SABRE has to compress the air to 140 atmospheres before injecting it into the combustion chamber. Without the new pre-cooler technology, that would raise the air temperatures high enough to melt engine materials.

Recent tests on SABRE involving over 100 test runs at the Reaction Engines facility in Oxfordshire have demonstrated the workability of the concept in the eyes of the European Space Agency, which has been funding part of the work. This Reaction Engines news release quotes ESA’s evaluation: “The pre-cooler test objectives have all been successfully met and ESA are satisfied that the tests demonstrate the technology required for the SABRE engine development.” The successful pre-cooler testing should allow the release of additional funding for the Skylon project from the British government according to an April 2011 agreement.

As for Alan Bond, he’s convinced Reaction Engines has proven its point:

“These successful tests represent a fundamental breakthrough in propulsion technology. Reaction Engines’ lightweight heat exchangers are going to force a radical re-think of the design of the underlying thermodynamic cycles of aerospace engines. These new cycles will open up completely different operational characteristics such as high Mach cruise and low cost, re-usable space access, as the European Space Agency’s validation of Reaction Engines’ SABRE engine has confirmed. The REL team has been trying to solve this problem for over 30 years and we’ve finally done it. Innovation doesn’t happen overnight. Independent experts have confirmed that the full engine can now be demonstrated. The SABRE engine has the potential to revolutionise our lives in the 21st century in the way the jet engine did in the 20th Century. This is the proudest moment of my life.”

You have to imagine that amidst that pride there is a bit of the old Daedalus excitement lingering in Bond’s work with Skylon, given that lowering launch costs by more than ten times is a necessary first step toward the infrastructure he foresaw as far back as the 1970s, when the Daedalus designers crunched numbers and sketched ideas at the Mason’s Arms pub on Maddox Street in London. But while Daedalus was speculative and, for its time, science fictional in its ambitions, Reaction Engines is now working with a design that could have a payoff in the not so distant future. We build out an infrastructure one step at a time, but the first step is to get into position. Cheap access to low-Earth orbit opens up scenarios that may one day take us far beyond our planet.

Although I see any work towards lowing the cost of space launch’s as a good thing. I believe the Scram-jet is a much more viable way to lower costs to orbit. It has less moving parts making it less prone to failure and it has been flown already, so it’s a somewhat proven technology. For all the failures of WaveRider plane, the Scram-jet itself never failed, the plane control services failed.

Keep hoping Mr. Bond takes seriously some of my emails asking him to begin designing Skylon II, to carry 12 passengers to the moon and back, after refueling in orbit. Bigalow Aerospace succeeding with their inflatable space habitats, (remembering von Braun’s inflatable space wheel of 1956) Bigalow’s first step building a private refueling station in orbit. Passenger trips to the moon and back might open the eyes of many political leaders. One world is one. Let’s return to the moon by 2025 at the latest…JDS

I’m glad to see them succeed at this important milestone. The Skylon and SABRE projects are one of the most exciting things to happen in aerospace tech in a while. That and SpaceX’s reusable rocket ambitions may put humanity’s space-faring dreams on track again.

And I’m also more that thrilled to see the impact that a person with a vision may have on the future of all. Cheaper access to orbit is really the enabler, still missing part required for serious manned space exploration and eventually, for Solar System’s settlement and exploitation.

And more specially in this case, where the person and the inspiration for innovation both came from participating in a precursor interstellar travel study as Daedalus. Thanks for pointing out this past affiliation, I was not aware of it.

This is fantastic news, and you are right to devote a posting to it. For years the bottleneck in space operations has been the expense and unreliability of access to space in the first place. The Shuttle was supposed to overcome this, but when it became apparent in the mid-1980s that the Shuttle was not the cheap, versatile space truck it was intended to be, America chose not to learn from it and develop the concept of reusable access to space further. Instead they declared it an operational vehicle and froze the design, except when occasional problems and accidents forced slight modifications. They proceeded to build the ISS, which needed just such a cheap, reliable vehicle for its maintenance, but whose high cost ensured that no funds were available to develop the Shuttle any further towards that vehicle. This is why we are now seeing private industry beginning to take up the slack and do the job that NASA was unable to complete.

Skylon and Sabre represent an interesting avenue of progress: there is no new physics here, no science-fictional concepts, just slow and steady progress in materials science and manufacturing capabilities, and extremely good engineering applied to the existing concepts of jet and rocket engine. Possibly a lesson for starship designers here?

Alan Bond and Tony Martin were of course also behind the 1984 worldship studies, which have inspired the latest issue of JBIS.

Allan Bond has been one of my heroes for more than thirty years . A long time before the internet I would sneak into a university library i Beer Sheva and feed lots of coins to an overworked copymashine , in order to follow the latest adventures of Allan Bond , mostly in ” Spaceflight News” . A one-man army of bright TALENT fighting against a world full of stupidity , bureaucratic red tape and corupt politicians . Most of his admireres lost hope 15 years ago when it became clear just how enormous the cooling probem was .
Some peoble just dont accept failure as an option …

Dear all,
It is indeed exciting news to see this development of the Skylon spaceplane. I note the comments from Greg about preferring scramjet technology, but there are reasons why RE have gone down their chosen approach and I believe it relates to performance. Alex I think each vehicle would be capable of around 200 flights.

The key technology has been the pre-cooler of course and with the European Space Agency stamp of approval, that was the last technical hurdle to SSTO becoming a reality. I say technical hurdle, because there is always that small issue of finance. Any philanthropists out there who want to secure themselves a legacy of having opened up space to the world at large?

Regarding Alan Bond and the Daedalus link. Yes, from what I understand the original suggestion for an interstellar flyby mission came from Bob Parkinson (Daedalus He3 gas giant mining man) in a letter to Alan Bond. Alan was looking for a project and then he got in touch with Anthony Martin. Those three were the creators behind Project Daedalus to my knowledge. The main purpose of Project Daedalus was to “prove that interstellar travel was feasible in theory”. The conclusion of the study was that if such a design was possible to conceive at the outset of the space age (1970s) then in 100 or 200 years from now a much more credible design must be possible and therefore interstellar travel was possible. The primary motivation here was to allow insight into the Fermi Paradox. For Project Daedalus the big issue was the requirement for gas giant mining which suggested the need for a solar system wide economy.

After Project Daedalus, Anthony Martin ended up as one of the Editors of JBIS, and did a terrific job editing some of the red cover issues, which ran between 1974 to 1991. Martin and Bond pioneered the 1984 World Ship papers as Stephen Ashworth mentioned. Alan Bond also did some work on interstellar ramjets, creating a modified Ram-Augmented Interstellar Ramjet. All these were published in JBIS, papers available for order from the web site:

3. He did the ice shielding calculations for the Arthur C.Clarke novel “The Songs of Distant Earth”, so Clarke would know how much thickness of ice was required for the generation starship.

Alan Bond was always a nuclear pulse propulsion fan, and from my numerous conversations with him this is I gather his favoured way of getting to the stars (Tony Martin’s too). But Alan soon realised after his Daedalus/World ship work that none of that is going to happen unless you open the door to heaven first – meaning cheap access to Earth orbit. Hence, he has spent the last couple of decades of his life dedicated to opening up space to the world through his SSTO approach. The man has given his life to space exploration and it gives me great pleasure to see Skylon happening in my lifetime.

@Greg – REL SABRE technology has a flight speed envelope from zero to orbital velocity and can operate in all regimes from ground air pressure to vacuum. This is better than having different engines or vehicles in each regime.

Your point about the recent US hypersonic test failures does show that having the engine does not mean that the airframe is a relatively simple project.

Well, someone has to be the kill joy and it looks like me.
Trying to cheat the rocket equation is like trying to rob Peter to pay Paul; it is such a fine trade-off that it never seems to work well enough to be practical.

I doubt it is worth the trouble. It was definiteley not worth it in the case of the space shuttle. Wasting the lift of a Saturn V class launcher to send a 737 sized hypersonic glider into orbit so it could come right back down turned out to be a very expensive dead end. Sadly, a cargo version that was always on the back burner would have made the shuttle program a success at any point in it’s 30 odd year career. It was never funded.
An airbreathing single stage to orbit launcher is a nice idea- but our gravity well is just a bit too deep. That’s the way the parabola bounces.

Tony D, as you say, it is strange that the space agencies are stuck in the 1960s. In my view, it is a question of organisational culture. NASA and its imitators (ESA) are wedded to the view that manned space travel, “for the foreseeable future, will remain difficult, dangerous and expensive” (quoting from memory from the CAIB report). This is regarded as having been proved by the Shuttle experience. Therefore only professional astronauts can fly in space. Therefore no large-scale market for personal space travel will exist for decades or centuries to come, and vehicles have no large-scale application and will remain unable to benefit from the reliability and cost advantages of such large-scale use.

The NewSpace point of view opposing this claims (with justification, in my view) that after 50 years of government exploration of orbit, the time is ripe to start developing a mass market for personal space travel, and thus to get onto the economic multiplier of rising traffic levels, falling unit costs and increasing reliability, as demonstrated by oceanic and more recently air travel. But since the space agencies do not expect this to happen anytime soon, let alone recognise any responsibility for stimulating its growth the way that governments foster economic activity in other areas, they have cut themselves off from any kind of market-led progress in space and are left basically trying to repeat the glory days of Apollo, until such time as the commercial sector completes the revolution begun by SpaceX, and now in prospect of transformation by Reaction Engines.

Regarding Daedalus, I would add that publication of the Daedalus report in 1978 essentially rendered the Drake Equation obsolete, by demonstrating that a scenario was feasible in which the set of locations in the Galaxy at which civilisation was found are dominated by colonies, not by natives. The Drake Equation, of course, makes the implicit assumption that interstellar colonisation does not happen to any significant degree, and is only valid while that assumption holds true.

@GaryChurch I think you have completely missed the point of re-usable SSTO.

The issue is not performance, but rather amortizing the cost of an expensive vehicle with frequent flights. Single use rockets incur both vehicle and ground handling costs. The high cost of throw away launches keeps frequency of flights low and incurs high facility costs. The space shuttle was a failure because it required much more work between flights than anticipated. Hardly airliner turnaround rates.

The industry needs a vehicle that works much more like an airplane. Costs are primarily fuel (v. cheap) and amortized capital. Reuse is a virtuous circle as the vehicle needs less testing after it has gone through initial checkout. This speeds turnaround, increases flight frequency and reduces the overhead costs.

The economics of the skylon plane might be better than it seems at first glance . At 26 km , the atmosphere has only a small fraction of its friction left , but how long will it take to climb out of the remaining friction-efect ?
This will depend on many interdependent factors , but IF the trajectory can be made steep enough , IF the oxygenburning mode of the Sabre engine has the POWER to do it , The skylon plane might achieve the best of both worlds , plane and rocket , and thereby even better economy than most predictions are talking about .
Another component of the initial plans was a ”rocket sled” that would acelerate the plane to 900kmh . This reduction in fuelweight could be translated to a bigger engine , enabling the steeper trajectory …

“Therefore only professional astronauts can fly in space. Therefore no large-scale market for personal space travel will exist for decades or centuries to come, and vehicles have no large-scale application and will remain unable to benefit from the reliability and cost advantages of such large-scale use.”

This is because professional astronauts tend to be from the military, and you can better control those folks, which is what the government wants. They do not necessarily want to give up space, but they are clearly not doing much to foster its real progress, either. Why do you think so much of the pie for space technology and utilization goes to military budgets? And not just the US government, either.

Nothing would be scarier to them than a group of private individuals or a corporation racing off into space on their own and founding colonies and businesses that are – gasp – independent of terrestrial control. Ignorance of the promise of space and science in general by most politicians play a role in this, too.

“Regarding Daedalus, I would add that publication of the Daedalus report in 1978 essentially rendered the Drake Equation obsolete, by demonstrating that a scenario was feasible in which the set of locations in the Galaxy at which civilisation was found are dominated by colonies, not by natives. The Drake Equation, of course, makes the implicit assumption that interstellar colonisation does not happen to any significant degree, and is only valid while that assumption holds true.”

I was in attendance at a SETI conference at Harvard University in 2000 with a number of the fields pioneers and bigwigs involved. The panel discussion started off with why aliens would not visit us in starships. They chose as their example a hand-drawn diagram of an antimatter-powered vessel with all the bells and whistles. It was simultaneously designed to show how complex, science fictiony, and just plain near-impossible (or at least very far off) interstellar travel would be for just about anyone, especially humanity.

They ignored any other forms of galactic transportation and launched into why aliens would conduct SETI and METI instead – and mainly the radio version at that, though optical SETI was just being allowed acceptance by the mainstream community at that time, nearly forty years after Charles Townes, the inventor of the laser, suggested it as a means of interstellar communications.

Anyone who does more than glance at Centauri Dreams knows that trying to get to even the nearest star system let alone anywhere else in the Milky Way galaxy is – especially if you want to go fast – rather difficult, to put it mildly. Electromagnetic transmissions by comparison are easier, cheaper, and much faster than anything we can do in regards to a starship right now or anytime soon. Even Daedalus’ vaunted controlled fusion proposal seems out of reach at present.

That being said, it must be noted how messy and dancing with the gray fringe territory talks of starships and aliens often get. Note the media and public focus on warp drives from the last 100 Year Starship Symposium. And UFOs are particularly dicey for both the professional starship builders and SETI camps. It is understandable at least why mainstream SETI has spent most of its history trying to keep the UFO crowd at long arm’s length. Radio is a much more respectable situation to deal with, not to mention safer than a giant spaceship suddenly appearing over a major city or such.

I think things have opened up a bit since those days that the possibility of alien probes in our Sol system monitoring us on the lowdown or galactic colonization was considered the stuff of science fiction and worse. The problem is that any concept faster than a Worldship has a lot of technological and physics hurdles to overcome, and certainly a Worldship is hardly free of major issues, either, despite not needing a warp engine.

So maybe it is rather tough to ply the stars, fast or slow. Maybe we’re one of the few that has even attempted it, and look how literally far we have to go. Maybe SETI is the answer to finding out what’s going on out there, but there are so many unknowns and we are still so new at this game. Maybe we do need someone to show up with the Encyclopedia Galactica and a spare hyperdrive.

Light-weight cryogenic heat exchangers are the bleeding edge technology for SABRE, and having spent a few years working on ACES (Air Collection and Enrichment Systems), I know how difficult and unforgiving this type of heat exchanger can be. If Allen has met the goals he was striving for a few years back, HOTOL should be successful. Best wishes to to the Reaction Engines team.

“GaryChurch I think you have completely missed the point of re-usable SSTO.”

No, I understand completely Alex; it is the airliner to space model that has been around for a very long time. Nothing new here.

The “point” is this- orbital speed is not the goal, escape velocity is. Getting to the moon with a worthwhile payload is the key to getting into space. LEO is just going in endless circles at very high altitude- going nowhere not fast enough. Chemical propulsion is appropriate for getting out of the magnetosphere without contamination the biosphere but that is all. The moon is the place to test, assemble, and launch the nuclear systems necessary to go anywhere in the solar system.
The holy grail is not Skylon or anything resembling it; there is no cheap.
What is required is a way around the need for an oxidizer and the only way to do that is beam propulsion. This line of reasoning ultimately ends with David Chriswells concept of Lunar Solar Power.
The same magnitude of power necessary to even begin to think about any interstellar mission. Which, by the way, is what this blog is about.

@GaryChurch. I think you are moving the goal posts. This was your statement: An airbreathing single stage to orbit launcher is a nice idea- but our gravity well is just a bit too deep.

To counter your argument:
1. The only existing commercial business to bootstrap off is orbital – primarily comsats. The driver is cost of access to space.
2. Once in orbit, there are either other propulsion technologies that will get you to escape velocity, e.g. electric. You can also use chemical propulsion and refuel in orbit. Nothing new there either. No beams required.

I think we should be very wary of single propulsion solutions. Or indeed any single technological solution.

“The only existing commercial business to bootstrap off is orbital – primarily comsats. The driver is cost of access to space.”

That is no counter to anything I wrote.
Like all the schemers and dreamers you cannot escape from the box you are trapped in- the money box. Whenever someone starts quoting economic formulae or strings of zeros it means only one thing; they are not going anywhere.

The reason to go into space is not filthy lucre. This is a question on which may hang the extinction or continuation of the human race. If money cannot be made then it will not happen is the common perception. It will not happen for money. The best way I have found to understand the problem is to look at the U.S. defense budget. It is so immense yet almost invisible to the public who do not question the vast mountains of treasure being expended on shiny cold war toys. It is true beyond any possible arguement that endless billions of dollars are consigned to endless lists of defense contracts.
Anyone who says we do not have the money to accomplish massive projects in space is a liar or ignoring the trillion dollars a year that disappears into the military.
The truth is that weapons and black projects are easy money; they often have no mission or cannot do the supposed mission they are intended for. They do not have to- mostly they just sit somewhere or are “classified.” I know from personal experience that much of the money spent on defense goes into programs that do not work as advertised or do not even work at all.
Spaceships are hard money- they have to work. No profit there.

“-other propulsion technologies that will get you to escape velocity, e.g. electric. You can also use chemical propulsion and refuel in orbit. Nothing new there either. No beams required.”

Private space propaganda has had the effect of making it seem all so easy. Electric propulsion will not get you through the Van Allen belts fast enough. So far only Hydrogen and Oxygen have the kick necessary to get people out there. The Rocket Equation is not going to change. As for “refueling in orbit”, that is the most magnificent job of pushing baloney ever accomplished. Repeat a lie enough and people believe it. Liquid hydrogen technology was perfected at tremendous expense but that technology does not include storing and transferring it in space. In fact- it has never even been attempted due to the nightmare plethora of problems that arise. It is ultra-cold exotic stuff that does not store well, requires pre-cooling with liquid helium to transfer, and since a transfer pre-cool cannot be done completely it generates boil-off. Re-liquifying the boil off results in the exothermic form of hydrogen which promulgates more boil-off in the storage tank. That is just the beginning; zero G effects and radiation make everything even more difficult.
This is why they store oxygen in high pressure tanks in the ISS. Hydrogen is not even a possibility.

Storable propellents make earth departure stages very large compared to hydrogen oxygen stages. What turns out to be the best solution is a Heavy Lift Vehicle just like the much maligned SLS. The Ayn Rand-space-club wail and gnash their teeth and dogpile anything that appears in the blogosphere criticizing their demi-god Musk and his hobby rocket tourist scam. But that does not change the fact that there is no cheap.

GaryChurch, just one point concerns me in your replies to Alex Tolley, and that is that your statement that “Electric propulsion will not get you through the Van Allen belts fast enough.”.

Are you sure that that could not be solved by the following two steps.
1 Increase apogee much more than perigee,
2 Transfer the crew on the last orbit by some very cheep mechanism (jetpack if you really have to)

If we needed a more sudden orbital transition on that last orbit we could also use the slingshot of the moon

Governments must for the most part provide public goods. One can argue over the level of defense spending, but the assumed good is public safety. It is very difficult to justify spending huge sums of public money on projects that do not benefit the taxpayers. Conversely, private entities can do what they like, and if profitable, can generate vast resources to apply to projects. A number of corporations now have revenues exceeding many nations. If there is no way to create an economy that extends into space, then a limited global GDP will limit the scope of space development. Global GDP growth will unlikely be sustainable to the levels needed for starlight.“Electric propulsion will not get you through the Van Allen belts fast enough. “
If you can only see a use for propulsion to move people, then you are correct, given current approaches. But there are ample opportunities to move cargo cheaply using low thrust propulsion.“As for “refueling in orbit”, that is the most magnificent job of pushing baloney ever accomplished. Repeat a lie enough and people believe it. “
See Nasa’s proposal here: Propellant Depot. Are you saying that Nasa is clueless?
“Storable propellents make earth departure stages very large compared to hydrogen oxygen stages. What turns out to be the best solution is a Heavy Lift Vehicle just like the much maligned SLS.”
I disagree. The key is reusable spacecraft. Reusable for ground to orbit. Reusable for space only. This allows for optimized designs for each environment. This also stimulates the virtuous circle of lowered cost and increasing demand.

Your ad hominem attacks on private space enterprise strike me as wanting to preserve the status quo, rather than having any real merit.

From your wiki citation:
“These study contracts for storing/transferring cryogenic propellants and cryogenic depots were signed with Analytical Mechanics Associates, Boeing, Lockheed Martin and Ball Aerospace. Each company will receive US$600,000 under the contract.[17]”

That’s it. The rest of it is just proposals. Studies to confirm it will not be practical is what they are. Like SSTO. They dumped a couple billion figuring out the NASP would not work. Of course these companies love to try and make their “proposals” work even though they defy physics- and common sense.

“private entities can do what they like, and if profitable, can generate vast resources to apply to projects.”

They generate profit, not resources. The resources are always there. Alex, you are playing a game here that anyone not brainwashed by trickle down voodoo infomercials can see right through.

“If there is no way to create an economy that extends into space, then a limited global GDP will limit the scope of space development.”

Nonsense. I already pointed out that vast resources are available for space development that are now expended on a more profitable market- the military. The military industrial complex is concerned with profit and as I stated, cold war toys are easy money because they don’t really have to work while spaceships are hard money.

There is no virtuous circle here. Your argument seems is actually to preserve the status quo. I am arguing to create progress, not preserve stagnation.

Reusability is a myth. It is why the RS-68 was built. The key to resuability is robust construction and maintainability. Both are impossible with rockets. Fill a egg thin container with super cold liquified gas, subject it to extremes of heat and vibration; it and the controlled bombs called rocket motors then get thrown away because it costs far more to inspect, rebuild, and fly them again. And anyway performing complex maintenance in space is not practical.
There is no unobtanium or wishalloy that is going to change that.

Alex Tolley, I disagree with most major points in your last comment (Dec7).

1 Money spent on safety can always be given as lives saved (or heath gained) per dollar spent. I have NEVER seen any analysis that claims a positive correlation for military spending. It is obviously it is about projecting power and prestige. This can occasionally be of benefit to all parties involved, but space expenditure seems like a much surer way of reaching these goals to me.

2 GaryChurch was obviously claiming that electric propulsion was limited if human exploration was a major factor, not that the Van Allen belts would destroy anything that lingered there.

3 To many of us the question is not whether propellant depots may be great half a century hence, it is what options can we work with right now

4 Is reusability really the be all and end all of cost reductions. I can’t help noticing that the cheapest and the heaviest bit of the shuttle was the external tank, and I am pretty sure that making it also recyclable would have ballooned costs.

@Rob Henry
It isn’t a matter of what makes economic sense, but what the voters will accept. Ideally the investment would have a positive economic gain. AFAIK, the multiplier on military spending is low. But individual voters can be persuaded that defense spending helps them. This is a much harder sell for space programs. Remember all that domestic spending vs Apollo moon landings in the 1970’s?

I don’t believe my reply that you refer to in point 2 implies that at all. GaryChurch was implying that all missions must be manned, whereas I am saying that there is plenty of room for unmanned missions, especially those that support manned missions. For example, sending fuel and supplies by cheaper cargo vessels to the target may make more sense that bringing everything you need in expensive vehicles, probably in one shot as implied by the requirement to achieve escape velocity. GaryChurch is making an argument that sounds like – “humans must use aircraft, therefore everything they need must be flown. No trains, trucks or ships can be used to delivery any component of their needs to their destination”. That makes no sense. If he is not arguing that, then there is room for other propulsion approaches. Also electric is not synonymous with slow. Magnetic launchers being just one possible future example.

If fuel depots do make sense, why would it take 50 years to put them in place?
Cannot we determine that within a decade and then start using them? Conversely, if you don’t build infrastructure, doesn’t it become easier to abandon the whole [costly] program? I personally think that water is the key. It is ubiquitous in the solar system. It can used directly as propellant mass for thermno-electric propulsion, or electrolyzed for chemical propulsion. It is the opportunities for in-situ resource utilization that is the game changer, reducing total costs. Add in frequent flights to amortize capital costs and the immense cost of space flight becomes just very large.

Yes, reusability and flight frequency is key. This is the basis behind all the private sub-orbital tourist flights. As we saw with Rutan’s design for Space Ship One, the airframe is fully reusable, and the hybrid engines are simply replaced for each flight. Recall that the X-Prize required a maximum 2 week turnaround time with the same vehicle. The economics is very basic.
Notice that GaryChurch puts himself in a self-imposed box by insisting that you must use LH2/LOX vehicles that are difficult to reuse and therefore reuse is impossible. Sure they cannot be refurbished in space – yet. But there is no inherent reason that they cannot, given the facilities.

@GaryChurch – we’ve looked at the numbers for starflight costs in other threads. The global economy has to be vastly larger (100’s x) to support it, which is why the projections are always many centuries out. But unless the global GDP can continue to grow to reach the required levels, it is not going to happen. Spending the total current US military budget each and every year will not get you a human crewed star ship, unless you have some way to make it very much cheaper than currently envisaged.
I really don’t understand why you have such antipathy towards private business, but economics requires that in order to grow the economy, investment must be productive, whether done by private or public means. Space development most certainly would be well down the list in this regard, despite the claims of spinoff technology.

If there is going to be a future for manned spaceflight (even unmanned), it is going to need more than national prestige to sustain it. Economic drivers are far more powerful.

@GaryChurch: I have to chip in here. We all know that lowering space access costs is key, and I don’t understand why you appear so angrily dismissive of NewSpace pioneers like SpaceX and Reaction Engines. You seem to have decided that significantly lowering the cost of space access via rapidly reusable reliable rockets (whether staged or SSTO) is just impossible, that it’s stupid to waste time thinking otherwise, and that is that.

I strongly disagree, and I think clear evidence for that is already available in the price lists for NewSpace expendable launch vehicles like Falcon 9 and the upcoming Falcon 9 Heavy.

Although we’ve seen many wonderful achievements since the success of Apollo, the primary goal should have been low-cost space access, and the old guard failed to reach it. It is now absolutely fair, with the greatest respect, to question the culture and received wisdom of old government agencies and the cartel of defence and aerospace corps they supported.

The old era of big-fish contractors supporting schools of cleaner-fish subcontractors and charging astronomically high prices should be done away with. We have to try new approaches.

We have to experiment, because we want to go and we’re tired of waiting. We need to go. And we will go.

Really? It would seem that spending MORE money on space access would be key. Like that one trillion that will be spent on the F-35 stealth fighter over the next half century. It does not work as advertised and never will but shareholder checks are going out. This piece of junk may eventually drop some million dollar bombs on some illiterate mountain tribesmen to justify it’s existence. Considering we have reusable solid rocket boosters that put out 3.6 million pounds of thrust ready for production but instead complain they cost too much and want to go cheap, I think your point is actually ridiculous.

I do not appear to be, I AM angrily dismissive. They are scamming the taxpayer. Hobby rockets and billionaut toursts are not a space program.

“You seem to have decided that significantly lowering the cost of space access via rapidly reusable reliable rockets (whether staged or SSTO) is just impossible, that it’s stupid to waste time thinking otherwise, and that is that.”

You seem to be mistaking Low Earth Orbit for deep space. You are talking about going in endless circles at very high altitude. I think it is a stupid waste of time to think that way. 30 years of tin cans going around and around is enough.

” It is now absolutely fair, with the greatest respect, to question the culture and received wisdom of old government agencies and the cartel of defence and aerospace corps they supported. ”

Fairness and respect have nothing to do with it. It is all about money. The “recieved wisdom” is that oversight and transparency is above all things the most important factor in space exploration. We know this by the Apollo 1 fire- probably the single most important event in the race to the moon. It took some people burning to death to make us hold the profit motive in contempt and demand the job be done rigtht. We know this from the Space Shuttle Program that used a single cooked-up think tank study to promise ridiculously low prices per pound to orbit. And the pressures to launch and budget cuts that prevented any escape systems being and killed two shuttle crews. There is no cheap.

As for Alex:
“-the economics is very basic.
Notice that GaryChurch puts himself in a self-imposed box by insisting that you must use LH2/LOX vehicles that are difficult to reuse and therefore reuse is impossible.”

It is not a self-imposed state of mind, it is the reality of the rocket equation and materials science. Like steam engines, we know the thermodynamic realities of rockets pretty well now. Everything revolves around exhaust velocity which I hope grasp through your advocacy of electric propulsion. Back in the 50’s ex-nazi/future nasa member Von Braun did calculations for reusing expensive rocket stages and came up with feeble payloads of a few tons delivered from massive lauch vehicles. Those calculations are just as valid today as they were then and lead to the same conclusion; our gravity well and rocket fuel exhaust velocities mean reusability is not practical. But there is obviously money to be made by lying about this and advertising the impossible.

The cost of payload (at the margin) is the cost per flight. The more you can reuse the vehicle and the more frequent the flights per vehicle, the lower the cost.

Rocket fuel is about $25/kg for payload. Published launch costs ~ $10k/kg. Thus the fuel costs are 0.25% of launch costs.

Suppose we get the economics to work more like an airline, which uses expensive vehicles that are kept in the air with minimal ground handling and repair. Airlines have about 6% of the costs as fuel. So perhaps we can get costs to LEO down to $(0.25/6) * 10K/kg < $500/kg, which puts a ticket to orbit at perhaps $100-200k.

That doesn't seem so far off the estimated prices (4x) for the Falcon 9H which is not even remotely flying at airline frequencies.

Then transfer to the hotel/interplanetary ship at LEO.

Perhaps it is unrealistic to expect comparable economics for space planes and aircraft. I do not know, as we do not have any real experience of it except with the Shuttle, which was clearly not satisfactory in this regard.
Just watching the tedious final checkouts of the Shuttle on Nasa tv made watching paint dry look exciting. Did it really require 6 people over an hour to seal the hatch, or was this "jobs for the boys"? Even Apollo was much simpler. One would hope that any future commercial passenger carrying vehicle could just close the hatch and lock it like an airliner.

The bigger question is whether access to space will have an elastic demand curve, or whether the skeptics are right that the only viable business is comsats which are fairly demand inelastic. The space entrepreneurs clearly hope that demand is ultimately elastic.

“Suppose we get the economics to work more like an airline, which uses expensive vehicles that are kept in the air with minimal ground handling and repair.”

Fantasy. You might as well be discussing star gates and hyperdrives Alex. You get to your “hotel” and what happens next? Since liquid hydrogen depots are not going to happen for a very long time (I do not think ever) if you want to go anywhere except in circles you will have to board a Earth Departure Stage using storable propellents. The Isp numbers for UDMH and N204 mean your ticket to the moon is going be about the size of Saturn V first stage. Understanding these numbers is why we made it to the moon; it is obvious that the most efficient way is a direct launch from Earth by way of a Heavy Lift Vehicle with hydrogen upper stages.
This is the first thing that anyone interested in space travel should comprehend; THERE IS NO SUBSTITUE FOR A HLV WITH HYDROGEN UPPER STAGES!
This is the second thing that anyone interested in space travel should comprehend; CHEMICAL PROPULSION WILL ONLY GET YOU TO THE MOON- NUKES ARE NEEDED FOR HSF-BLO (human space flight beyond lunar orbit).
And this is the third thng that anyone interested in space travel should comprehend; MASSIVE GOVERNMENTAL RESOURCES ARE REQUIRED TO BUILD ATOMIC SPACESHIPS CAPABLE OF ESTABLISHING OFF WORLD COLONIES!
It is not the airlines and tourists are not going to Mars. It is a scam. There is no cheap.

They clearly hope that the public remains as stupid as they are for believing the fairy tales they are telling.

Any space program that can be called such begins where Apollo left off- with at least a Heavy Lift Vehicle launching every month landing payloads on the moon near ice deposits. There is no flexible path- it is very direct and determined by physics to be possible with the appropriate technology and massive funding. So far “new space” is just a way to funnel tax dollars into those “enterpreneurs” pockets for nothing in return.

@ Alex
“If fuel depots do make sense, why would it take 50 years to put them in place?
Cannot we determine that within a decade and then start using them? Conversely, if you don’t build infrastructure, doesn’t it become easier to abandon the whole [costly] program? I personally think that water is the key. It is ubiquitous in the solar system. It can used directly as propellant mass for thermno-electric propulsion, or electrolyzed for chemical propulsion. It is the opportunities for in-situ resource utilization that is the game changer, reducing total costs.”

We are both believers Alex- it is like people in the age of steam argueing whether steamships would overtake sailing ships, or near the end of the 19th century when people argued about heavier than air machines surpassing lighter than air machines. Basically all our tax money now goes into weapons. Did you ever wonder where the sport of boxing comes from? Clockmakers. Germans. They invented some very simple and dependable clock windings and these made dandy ignition systems for the first concealable handguns. Well, these handguns come along and suddenly body armor is useless and when people stop wearing body armor they could be killed with a much lighter weapon. Instead of a pike pushed from behind by a second line of pikeman, and behind him a third- all that was required on bare skin was a flexible rod of steel with a very sharp point. Instead of a hand held shield as carried by the last of the fully plate armored swashbucklers, after handguns fighting men were naked except for the round bell of the spanish cup hilt rapier. This period in Europe saw some of the most violent religious wars in history. The most revolutionary weapons were guns- big and small. The classic French Musketeer was a specialist warrior carrying a huge shoulder fired weapon fired from a forked rest stuck in the ground. Fighting with these long thin bladed swords became the most deadly of all Western Martial Arts; fencing. Due to English common law, it just so happened that men did not fight it out with hand weapons anymore- Rich or poor, rich against poor or poor against rich, deadly single combat was a crime to engage in. You had a responsibility to run away under the new law. Fisticuffs became the only violent act not sanctioned by the law because it was admitted that a man had a right to defend himself with non-lethal force. There were still staged non-lethal matches that could be bet on and these included unarmed fighting-boxing. A certain prizefighter who was also a fencer applied fencing principles to boxing and modern boxing as we know it became extremely popular. The whole sweet science of boxing is to knock a man down with a fast sharp hand strike to the head or solar plexis. Clocks to Boxing.
Those German clockmakers became German rocket makers and we have not progressed beyond what they achieved in the early 1960’s; over half a century has gone by. There are no more fundamental discoveries to be made about propulsion in any form; The two most important reactions for propulsion systems is chemical, with liquid hydrogen and oxygen giving the highest exhaust velocity, and nuclear in the form of Fission and Fusion. Immediately available to us is chemical propulsion- but storable propellents have a lower exhaust velocity than hydrogen and oxygen- and slow Fission reactors to provide electricity. There are several proven space reactor designs that could be returned to production. But while slow fission reactors can heat up propellent and give about double the isp of hydrogen and oxygen, this is still not really enough to get around the solar system.

This leaves only one immediately available and proven interplanetary propulsion system; bombs. The same military that gave birth to the ultimate weapon at the very same time gave us our greatest hope for the future. Of course H-bombs (fusion reactions) can incinerate a million human beings in about one second and are the classic two edged sword. We can use them to travel to other worlds or we can blow up the only one we have right now.

Wait . . . What? Did you post in the wrong comments area or something? Although I am not familiar with some of the aerospace concepts bandied around here, 17th Century Warfare is something I can tackle on Centauri Dreams for once!

Concealable handguns weren’t meant for battlefield use to begin with. They were meant to kill unprotected people at close ranges, so defeating armor was never an issue and they weren’t even terribly effective. They were considerably less powerful than the full sized arquebus matchlocks of the era, and to say that they rendered armor ineffective absolutely ridiculous. Armor fell out of fashion because firearm calibers had increased for a time during the period (with the Thirty Years War era musket, as you mentioned, needing a monopod to safely fire), and increasing the thickness of breastplates while maintaining quality simply became economically untenable for foot soldiers. Only the really wealthy could afford the stuff, and there’s a very good reason why the Count of Tilly was also known as the Monk in Armor. It has nothing to do with a certain Chow Yun-fat movie.

Armor was still worn by musketeers and pikemen on many occassions, however. Your claim that men fought “naked” or primarily with swords during the appropriately named Pike-and-Shot era is just plain silly, as is any conclusion developed from it. The use of pikes also quite specifically precluded effective swordplay unless your a pike square was in the process of running away. They carried short swords, but seldom actually used them. Dropping a 16 foot long pike while getting steamrolled by an enemy hedge was seldom practical, and neither was charging into a pike square with a sword to begin with. Mythical depictions of pike slicing Zweihander wielding mercenaries be damned!

And did you leave out the time honored, often fatal practice of pistol dueling?

Let us not forget that there are very few nations that actually spend more of their budgets on defense than anything else. The claim that, “all our tax money now goes into weapons” is a bald faced lie. Only ~20% percent of the federal budget (a scant 4.7% of the GDP!) goes into military spending in the U.S., and Social Security and Medicare/Medicaid in fact consume far more. The U.S. spends far more on the latter than most other western nations, so why not cut that spending? Most of that military budget isn’t even for R&D and weapons manufacturing: It’s on maintaining existing equipment (so you don’t NEED to make replacements) and paying wages.

Yet since when is this a history blog? You could have made a more relevant point by comparing the development of gunpowder rockets or coaling stations and the first all-steel ships to the proliferation of regular cislunar traffic, but you did not and I suspect that this would have actually supported the underlying architecture that Skylon ultimately seeks to enable ala NASA’s Space Transportation System (reusable cislunar space vehicles, propellant depots, etc.). Getting to Mars with chemical rockets is totally possible if you start in LEO or beyond where the mission Delta-V is more reasonable. Though getting back may require some imaginative in situ development or deploying cryogenic storage technology, this is a lot more tenable than setting off dozens of nuclear weapons in orbit. In many ways, near-future nuclear thermal nuclear rockets are still going to have the same problems with transferring to Mars as traditional chemical rockets do.

“defeating armor was never an issue and they weren’t even terribly effective.”

I read a different history book obviously. I have to disagree that “defeating armor was never an issue.” Blowing a hole in someone was and is the whole issue.
-and to say that they rendered armor ineffective absolutely ridiculous.”

Guns shoot through armor. Which is why cavalry carried pistols in that era.

“Your claim that men fought “naked” or primarily with swords during the appropriately named Pike-and-Shot era is just plain silly”

Naked to gunfire. They did not think it was silly.

“this is a lot more tenable than setting off dozens of nuclear weapons in orbit. ”

Nuclear weapons going off in lunar orbit is ideal. Keeping nuclear material safe anywhere within the magnetosphere is the requirement.

Cavalry tended to carry pistols, but that didn’t mean they were terribly useful. Pistols are already of questionable value on the battlefield, and shooting them at decidedly long range made them even worse. They were unlikely to HIT their targets outside a few paces (wherein cavalry produces a large target for musket balls and pikes), let alone produce a fatal wound on an unarmored person! That’s precisely why marginally more effective carbine toting dragoons ended up completely replacing them during the course of the Thirty Years War. Keep in mind that pistoleers typically wore armor and tried to purchase more if possible, and dedicated heavy cavalry still existed in force via cuirassiers. Surely you did not miss the many period illustrations of these armored fighting soldiers?

And of course, keep in mind that the phrase “bullet proof” dates back to when armor for said soldiers was tested by shooting it with a good arquebus and leaving the dent as a “proof”. Proofing against an enormous musket was a little more difficult, but armor was still quite common to pikemen and other infantry during the English Civil War and such.

And if you want to fire off Orion-esque drives in LLO instead of LEO, is that not further support for a reusable infrastructure? Getting the nuclear fuel to the Moon in one giant step every mission would be rather difficult, to say nothing of the vehicle in question. If launch costs to LEO can be reduced, you could conceivably reduce transfer costs to anywhere else in the Earth-Moon System.

“Getting to Mars with chemical rockets is totally possible if you start in LEO”

The last mission profile I read had a 100 ton Earth Departure Stage. There was no mention of how much radiation shielding the crew would have or if they had an artificial gravity system. The will suffer some permanent bone loss and serious debilitation without artificial gravity; without massive shielding on the order of a couple hundred tons the first bad solar event that heads their way will kill them if mutated pathogens do not do them in first.

Chemjical Propulsion will only get you to the Moon. Nukes are required for Human Space Fight- Beyond Lunar Orbit. The mass of radiation shielding removes any possibility of chemical propulsion being practical. The possible exception is launching a beam propelled stage from the Moon and use aerobraking to slow down on arrival to Mars. But that would require large solar power installations and antennae fields on the moon. And you might boost your way to Mars this way with a couple thousand Isp beam propelled Lunar Departure Stage but you have to get back.

In any case all the really interesting places to go- low gravity icy moons- are in the outer solar system. Mars may seem “just close enough” and being a planet may seem to make it more hospitable in some way but this, like resuability, is a myth.
Bombs are the only way to carry a massive shield and get out past the asteroid belt and back within the psychological limits of the crew- which are probably around 5 or 6 years.
I do not think this situation is going to change when they inflate some playboy clubs for going in endless circles at very high altitude. Of course Private space advertises it that way.

“Getting the nuclear fuel to the Moon in one giant step every mission would be rather difficult, to say nothing of the vehicle in question.”

Actually, a couple hundred survivably packaged “pits” can be sent to the moon in a human-rated capsule with a very powerful escape system on the SLS. That is as safe as it gets and after a hundred and thirty shuttle missions with no escape system and with packaging designed to survive vehicle failure that is the risk that must be accepted. A typical deep space mission lasting 5 or more years would require a couple thousand of these pits. This nuclear material represents the base fuel that when formed for a pulse unit system has an Isp so far beyond any chemical fuel that you must admit any comparison is completely ridiculous.

While electric systems have high Isp’s, comparing their typically ounces of thrust to a bomb is even more ridiculous. Even more ridiculous than arguing about the prevalence and relevance of armor in the age of pike and shot. My little story about German clockmakers was meant to illustrate that the reasons the way things are the way they are is complicated and so is the reasoning behind much of what we choose not to accomplish in space.

As for the vehicle in question, the Moon has high quality ore to build alloy pusher plates in the thousands of tons range required- and thorium to fuel reactors for use in deep space. But in the short term thin discs can be sent to the moon on HLV’s and stacked to form thicker plates to construct the initial spaceships for the first bomb propelled deep space missions. The best destination for this mission is Ceres in my opinion. You can read more of my desperate plan to save the planet at-

SSTO possible with what Reaction engine is trying we will see even new airplane designs have made the possible SSTO closer see the new double box tail design a ground breaking improvement in fuel lift drag reduction combined with a reaction air breathing engine will work you people forget the x plane with a million lb thrust rocket engine it was heat shielding that was the problem there will be no nuclear spaceships the weight makes that impossible lead shielding. plasma converters for electricity using a version of Chang Diaz`s plasma rockets (ion engines) will open up the solar system if everyone was like Gary cell phones T.V. radio, flight its self is impossible how many people said the wright brothers were nuts it will never fly the only thing for sure is that man never knows what can be done or what he can do until he tries Gary also leaves out the assist of lift with any plane not something you will be able to take advantage of from a vertical rocket what ever the means they must be compressing hydrogen in a tank some how where was the hydrogen the Shuttle was using in a tank some where the problems you talk about for compressing hydrogen is the same for compressing any gas any scuba diver can tell you about how that works keep in mind any one who said i can not be done nine times out of ten are just wrong i have had people in my life tell me that i could not do things that i had already done so if some one says it cant be done it really means that they cant do it

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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